(1) Field of the Invention
The present invention relates to a process for nitriding an aluminum-containing substrate.
(2) Description of the Related Art
As wirings in the semiconductors and liquid crystal panels become finer, fine workings with dry processings are progressing. With the demand for such fine workings, halogen-based corrosive gases are used as film-forming gases or etching gases for the semiconductors and the like. On the other hand, it is known that aluminum nitride exhibits high corrosion resistance against such halogen-based corrosion gases. Therefore, members having aluminum nitride on their surfaces have been used in semiconductor-producing apparatuses, liquid crystal panel producing apparatuses and the like. More specifically, there are available powdery aluminum nitride-sintered materials, materials in which an aluminum nitride film is formed on a substrate by using a vapor deposition such as CVD, and materials in which a surface of aluminum is modified and aluminum nitride is formed thereon.
When aluminum contacts air, its surface is oxidized to form a thin oxidized film. Since this oxidized film is an extremely stable passive phase, the surface of aluminum can not be nitrided by a simple nitriding method. Under the circumferences, the following methods have been specially developed to modify the surface of aluminum and form aluminum nitride thereon.
JP-A-60-211061 discloses a method in which after the inner pressure of the chamber is reduced to a given level and hydrogen or the like is introduced thereinto, discharging is performed to heat the surface of aluminum to a given temperature, further argon gas is introduced and discharging is performed to activate the surface of aluminum, and the surface of the aluminum is ionically nitrided through introducing nitrogen gas.
JP-A-7-166321 discloses a method in which a nitriding aid made of aluminum powder is contacted with the surface of aluminum, and aluminum nitride is formed on the surface of aluminum through heating in a nitrogen atoms-containing atmosphere.
However, according to the method described in JP-A-60-211061, since aluminum nitride is formed by using discharging, the entire device is complicated to raise the cost. Further, it is difficult for this method to nitride members having complicated shapes or large sizes.
Furthermore, according to a method described in JP-A-7-166321, since a nitriding aid is used, voids exist in a resulting surface layer of aluminum nitride so that denseness is not sufficient. For this reason, it is an actual situation that corrosion resistance of the surface against the halogen-based corrosive gas is not sufficient and not practicable.
Moreover, when sintered aluminum nitride is to be used, since aluminum nitride powder is necessary to be sintered at a high temperature and the sintered body is difficult to be worked, there is a problem of a high cost. Further, it is extremely difficult to form members having large sizes or complicated shapes. In the case that aluminum nitride is formed by CVD process, there are such problems that members having large sizes or complicated shapes are difficult to be formed, and the device and the process are complicated and expensive.
NGK Insulator, Ltd. discloses a technique in Japanese Patent Application No. 11-059011 (JP-A-2000-290767), in which surface of aluminum by heating the aluminum in the nitrogen atmosphere immediately after heating it in vacuum. However, depending on various conditions such as the shape of a container and the number of times of growing the films, the quality of the nitride film is degraded, or the growing rate of the film is decreased, or, in some cases, the nitride film is extremely difficult to be grown. For this reason, the technique may cause a disadvantageously large fluctuation as a nitride film producing method.
It is an object of the present invention to provide a process for producing a nitride film with a stable quality, when the nitride film is formed on an aluminum containing substrate.
It is another object of the present invention to reduce a fluctuation of a film forming state of the nitride film, when the nitride film is formed on an aluminum-containing substrate.
The first aspect of the present invention relates to a process for nitriding a substrate containing at least metallic aluminum, said process comprising the steps of heating the substrate in vacuum of 10xe2x88x923 torr or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously to said heating step, wherein a porous body through which a nitrogen atoms-containing gas can flow is clarified by heating at a temperature of 1000xc2x0 C. or more under a pressure of than 10xe2x88x924 tort or less and then contacted with the atmosphere during the heating/nitriding step.
The second aspect of the present invention relates to a process for nitriding a substrate containing at least metallic aluminum, said process comprising the steps of heating said substrate in vacuum of 10xe2x88x923 ton or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously to said heating step, wherein said heating/nitriding step is repeated two or more times and an amount of each of magnesium, lithium and calcium absorbed by said porous body is controlled to 0.5 ppm or less before subjecting it to the next heating/nitriding step.
The third aspect of the present invention relates to a process for nitriding a substrate containing at least metallic aluminum, said process comprising the steps of heating said substrate in vacuum of 10xe2x88x923 torr or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously to said heating step, wherein said heating/nitriding step is performed after a structural body of a furnace body for said heating/nitriding step is clarified by heating at a temperature of 1000xc2x0 C. or more under a pressure of 10xe2x88x924 torr or less.
The forth aspect of the present invention relates to a process for nitriding a substrate containing at least metallic aluminum, said process comprising the steps of heating a substrate containing at least metallic aluminum in vacuum of 10xe2x88x923 torr or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously to said heating step, wherein said heating/nitriding step is repeated two or more times and an amount of each of magnesium, lithium and calcium absorbed by said structural body of the furnace body is controlled to 0.5 ppm or less before subjecting it to the next heating/nitriding step.